A Theoretical Evaluation of Ultrasonic Detection of Small Gas Bubbles.
Abstract
The scattering of ultrasound (such as is commonly used in medical diagnosis) by small bubbles was analyzed. A bubble larger than the acoustic wavelength casts an acoustic shadow as predicted by geometric acoustics; a bubble the same size as the acoustic wavelength imparts strong directionality to the scattered wave. A bubble smaller than the acoustic wavelength radiates a scattered spherical wave of less than 0.1% of the incident energy because of dissipative losses. For a random distribution of these bubbles (of sub-wavelength size) the intensity of the scattered wave is directly proportional to the bubble density. A direct acoustic-optical imaging system (ultrasonic Bragg imaging) is insufficiently sensitive to detect bubbles smaller than an acoustic wavelength. The image detail in acoustic-optical imaging systems is limited by the acoustic wavelength, the numerical aperture of the optics, and spatially abrupt near-field acoustic intensity variations. (Modified author abstract)
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 01, 1972
- Accession Number
- AD0784369
Entities
People
- William M. Carey
Organizations
- Naval Medical Research Center